Wiring film and active matrix substrate using the same, and method for manufacturing wiring film

ABSTRACT

An Al wiring film having a tapered shape is obtained easily and in a stable manner. An Al wiring film has a double-layer structure including a first Al alloy layer made of Al or an Al alloy, and a second Al alloy layer laid on the first Al alloy layer and having a composition different from a composition of the first Al alloy layer by containing at least one element of Ni, Pd, and Pt. The second Al alloy layer is etched by an alkaline chemical solution used in a developing process of a photoresist, and an end portion of the second Al alloy layer recedes from an end portion of the photoresist. Thereafter, by performing wet etching using the photoresist as a mask, a cross section of the Al wiring film becomes a tapered shape.

FIELD OF THE INVENTION

The present invention relates to a structure of a wiring film containingaluminum and a method for manufacturing the same, and more particularlyto a wiring film applicable to an electrode of a thin-film transistorprovided on an array substrate or the like of a liquid crystal displayapparatus.

DESCRIPTION OF THE BACKGROUND ART

For example, aluminum (Al) is known as a material of a wiring film usedas an electrode of a thin-film transistor that is formed on an arraysubstrate (active matrix substrate) of a liquid crystal displayapparatus. Since an electric resistance of Al is very low, it has beengenerally used as a wiring material conventionally. In thisspecification, a film obtained not only from pure Al but also a materialcontaining Al as a main components such as an Al alloy, and a wiringfilm resulted from patterning such a film are broadly referred to as an“Al film” and an “Al wiring film”, respectively.

A wet etching method using a chemical solution containing phosphoricacid and nitric acid series is common as a method of pattern process(patterning). However, since the method is isotropic etching, a sidewallof an Al wiring film resulted from patterning becomes substantiallyvertical. This causes an insulating film formed on the Al wiring film tohave a poor step coverage characteristic, and, as a result, causesbroken wiring of a wiring film formed on the insulating film, areduction of a breakdown voltage of the insulating film, or the like.

A technique for etching the Al film in a tapered shape is proposed tosolve such a problem in, for example, Japanese Patent ApplicationLaid-Open Nos. 06-122982, 2001-77098, 2003-127397, and 2007-157755.However, when a composition of a chemical solution (etchant) changes asan etching process progresses or degrades by time in such a technique,an inclination of the sidewall of the tapered Al wiring film acutelychanges accordingly. This poses a problem of a difficulty in managingthe composition of the etchant.

According to the general wet etching technique for the Al film describedabove, the sidewall of the Al wiring film subjected to the patterningbecomes substantially vertical. This causes the insulating film formedon the Al wiring film to have a poor step coverage characteristic, and,as a result, causes a reduction of a breakdown voltage of the insulatingfilm, broken wiring of the wiring film of an upper layer, or the like,which eventually causes a drop in the yield of the product.

Japanese Patent Application Laid-Open Nos. 06-122982, 2001-77098,2003-127397, and 2007-157755 propose an etching technique for formingthe Al wiring film in a tapered shape. However, it is necessary toseverely manage the composition of the etchant to obtain a predeterminedtapered shape in a stable manner. To do so, it is necessary, forexample, to introduce a facility to constantly monitor the concentrationof the etchant, or replace the etchant more frequently, which eventuallyincreases the cost.

Further, when an ordinary Al film is used as an electrode of a thin-filmtransistor (TFT) of an active matrix substrate for a liquid crystaldisplay apparatus, contact characteristics between the TFT and a pixelelectrode are drastically degraded due to an interface reaction with anITO film which is a transparent pixel electrode. For this reason, it isdifficult to apply the Al wiring film as a wiring film on the activematrix substrate.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a structure of an Alwiring film and a method for manufacturing the same, from which atapered Al wiring film can be obtained easily and in a stable manner,and which can be applied to an active matrix substrate of a displayapparatus.

A wiring film according to a first aspect of the present inventionincludes a first layer and a second layer laid on the first layer. Thefirst layer is made of Al or an Al alloy. The second layer is made of anAl alloy containing at least one element of Ni, Pd, and Pt and having acomposition different from a composition of the first layer. The wiringfilm has a tapered shape in cross section with a width smaller in anupper portion thereof than a width in a bottom portion thereof.

A wiring film according to a second aspect of the present inventionincludes a first layer, a second layer laid on the first layer, and athird layer laid on the second layer. The first layer is made of a firstAl alloy containing at least one element of Ni, Pd, and Pt. The secondlayer is made of a second Al alloy containing nitrogen. The third layeris made of a third Al alloy containing at least one element of Ni, Pd,and Pt. The wiring film has a tapered shape in cross section with awidth smaller in an upper portion thereof than a width in a bottomportion thereof.

A method for manufacturing a wiring film according to a third aspect ofthe present invention includes the following steps. A step of forming afirst layer made of Al or an Al alloy. A step of forming, on the firstlayer, a second layer made of an Al alloy containing at least oneelement of Ni, Pd, and Pt and having a composition different from acomposition of the first layer. A step of coating a photoresist on thesecond layer and performing exposure using a photomask. A step ofdeveloping the photoresist after performing the exposure and etching thesecond layer by using an alkaline chemical solution, so that an endportion of the second layer under the photoresist after the developingrecedes from an end portion of the photoresist. A step of forming thewiring film including the first and second layers by etching andpatterning the first and second layers simultaneously by wet etchingusing the photoresist after developing as a mask.

A method for manufacturing a wiring film according to a fourth aspect ofthe present invention includes the following steps. A step of forming afirst layer made of a first Al alloy containing at least one element ofNi, Pd, and Pt. A step of forming, on the first layer, a second layermade of a second Al alloy resulted from adding nitrogen to the first Alalloy. A step of forming, on the second layer, a third layer made of thefirst Al alloy. A step of coating a photoresist on the third layer andperforming exposure using a photomask. A step of developing thephotoresist after performing the exposure and etching the third layer byusing an alkaline chemical solution, so that an end portion of the thirdlayer under the photoresist after the developing recedes from an endportion of the photoresist. A step of forming the wiring film includingthe first, second, and third layers by etching and patterning the first,second, and third layers simultaneously by wet etching using thephotoresist after developing as a mask.

According to the present invention, the tapered shape of the Al wiringfilm can be stabilized without a need to manage the etchant stricterthan in the conventional case. Accordingly, the step coveragecharacteristic of the gate insulating film formed on the Al wiring filmis improved, it is possible to prevent the breakdown voltage fromreducing and the wiring film in the upper layer from breaking, and theyield of the product is improved. In addition, since the second layermade of an Al alloy containing at least one element of Ni, Pd, and Ptcan obtain an excellent contact characteristic with an oxide materialused as a transparent pixel electrode, it is easy to apply the wiringfilm to an electrode of a thin-film transistor provided in an activematrix substrate of a display apparatus.

According to the present invention, the tapered shape of the Al wiringfilm can be stabilized without a need to manage the etchant stricterthan in the conventional case. Accordingly, the step coveragecharacteristic of the insulating film formed on the Al wiring film isimproved, it is possible to prevent the breakdown voltage from reducingand the wiring film in the upper layer from breaking, and the yield ofthe product is improved. In addition, since the layer made of an Alalloy containing at least one element of Ni, Pd, and Pt can obtain anexcellent contact characteristic with an oxide material used as atransparent pixel electrode, it is easy to apply the wiring film to anelectrode of a thin-film transistor provided in an active matrixsubstrate of a display apparatus.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a structure of an Al wiring filmaccording to a first preferred embodiment;

FIGS. 2 to 4 are manufacturing process diagrams of the Al wiring filmaccording to the first preferred embodiment;

FIG. 5 is a graph indicating a relation between a composition ratio ofNi, Pd, and Pt of an Al alloy and an etching rate with respect to a TMAHorganic alkaline chemical solution;

FIG. 6 is a plan view of a structure of a principal portion of a TFTactive matrix substrate according to the first preferred embodiment;

FIG. 7 is a cross sectional view of a structure of a principal portionof the TFT active matrix substrate according to the first preferredembodiment;

FIGS. 8 to 11 are manufacturing process diagrams of the TFT activematrix substrate according to the first preferred embodiment;

FIG. 12 is a cross sectional view of a structure of an Al wiring filmaccording to a second preferred embodiment;

FIGS. 13 to 15 are manufacturing process diagrams of the Al wiring filmaccording to the second preferred embodiment; and

FIG. 16 is a cross sectional view of a structure of a principal portionof the TFT active matrix substrate according to the second preferredembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Preferred Embodiment

FIG. 1 is a cross sectional view of a structure of an Al wiring filmaccording to a first preferred embodiment. As illustrated in FIG. 1, anAl wiring film 101 formed on a substrate 100 according to this preferredembodiment has a double-layer structure including a first Al alloy layer101 a and a second Al alloy layer 101 b formed thereon, and has atapered shape in cross section with a width smaller in an upper portionthereof than a width in a bottom portion thereof.

The first Al alloy layer 101 a is a layer including Al as a maincomponent. This is not restricted to the Al alloy, but pure Al may alsobe used. The second Al alloy layer 101 b is made of an Al alloycontaining at least one element of nickel (Ni), palladium (Pd), andplatinum (Pt). The composition of the Al alloy of the first Al alloylayer 101 a is different from the composition of the Al alloy of thesecond Al alloy layer 101 b.

In addition, the substrate 100 serving as a base for the Al wiring film101 may be a semiconductor substrate such as a silicon substrate, aninsulating substrate such as a glass substrate used as an active matrixsubstrate for a display apparatus, or an interlayer dielectric filmprovided on another wiring layer.

Hereinafter, a method for manufacturing the Al wiring film 101illustrated in FIG. 1 will be described. FIGS. 2 to 4 are manufacturingprocess diagrams thereof.

First, the first Al alloy layer 101 a made of Al or an Al alloy isformed on the substrate 100. Formed on top of it is the second Al alloylayer 101 made of an Al alloy containing at least one element of Ni, Pd,and Pt and having different composition from that of the first Al alloylayer 101 a (FIG. 2). In this preferred embodiment, Al is formed into afilm having a thickness of 200 nm as the first Al alloy layer 101 a, andthe Al alloy resulted from adding 3 mol % Ni to Al is formed into a filmhaving a thickness of 20 nm as the second Al alloy layer 101 b bysputtering using an Ar gas.

Thereafter, a photoresist 102 having a predetermined pattern is formedon the second Al alloy layer 101 b using a photoengraving technique(FIG. 3). In this preferred embodiment, a positive type photoresist of anovolak resin is coated by a slit coater or a spin coater to a thicknessof 1.6 μm and is exposed using a photomask. Subsequently, the resultantis developed using an alkaline chemical solution to form the photoresist102 having the predetermined pattern. In this preferred embodiment, anorganic alkaline developing solution (liquid temperature of 23° C.)containing 2.4 wt % of tetramethylammonium hydroxide (TMAH) is used asthe alkaline chemical solution.

Here, since the Al alloy containing at least one element of Ni, Pd, andPt is etched by the alkaline chemical solution, the second Al alloylayer 101 b exposed from the photoresist 102 is etched in a developingprocess of the photoresist 102. The second Al alloy layer 101 b(thickness of 20 nm) containing 3 mol % Ni used in this preferredembodiment is etched by the TMAH organic alkaline developing solution atan etching rate of about 60 nm/min. Therefore, when the developingprocess is extended by 20 seconds after the photoresist 102 isdeveloped, a portion of the second Al alloy layer 101 b exposed from thephotoresist 102 is removed.

When the developing process is further extended, the second Al alloylayer 101 b under the photoresist 102 is etched in a transversedirection (in-plane direction of the film), and, as illustrated in FIG.3, a width of the second Al alloy layer 101 b becomes smaller than awidth of the photoresist 102. This means that ends of the second Alalloy layer 101 b individually recede from ends of the photoresist 102.

In contrast, the first Al alloy layer 101 a made of Al is hardly etchedby the organic alkaline developing solution containing TMAH. As aresult, notches 103 having an undercut shape are formed between thephotoresist 102 and the first Al alloy layer 101 a caused by receding ofthe ends of the second Al alloy layer 101 b.

Thereafter, in wet etching using the photoresist 102 as a mask, thefirst Al alloy layer 101 a and the second Al alloy layer 101 b aresimultaneously subjected to etching and patterning, so that the Alwiring film 101 having the predetermine pattern is formed (FIG. 4). Inthis preferred embodiment, an etchant of PAN series (phosphoric acid,acetic acid, and nitric acid series) is used for the wet etching.

During this process, since a notch shape is provided under thephotoresist 102, the ends of the second Al alloy layer 101 b and anupper surface of the first Al alloy layer 101 a are isotropicallyetched. Specifically, the upper surface of the first Al alloy layer 101a is etched while the ends of the second Al alloy layer further recede.As a result, the sidewall of the Al wiring film 101 is inclined, and theAl wiring film 101 has a tapered shape with a width smaller in the upperportion than a width in the bottom portion.

Finally, by removing the photoresist 102, the Al wiring film 101illustrated in FIG. 1 is completed.

Since the Al wiring film 101 according to this preferred embodiment hasa tapered shape, it is possible to have a good step coveragecharacteristic when an insulating film is formed thereon. Accordingly,this prevents the breakdown voltage of the insulating film fromreducing, prevents the wire of the wiring film in the upper layer frombreaking, and contributes to improvement of the yield of the product.

Further, since a process of patterning the Al wiring film 101 into atapered shape can be performed during the isotropically etching of thefirst Al alloy layer 101 a and the second Al alloy layer 101 b, thetapered shape (inclination of the sidewall) of the Al wiring film 101 ishardly affected by the change of the composition of the etchant.Therefore, the Al wiring film 101 having a predetermined tapered shapecan be obtained easily and in a stable manner without a need to managethe etchant stricter than in the conventional case. Accordingly, thecost incurred in managing the etchant does not increase.

Although the Al alloy containing 3 mol % Ni is used as the second Alalloy layer 101 b in this preferred embodiment, the application of thepresent invention is not restricted to this. An Al alloy film serves asthe second Al alloy layer 101 b if at least one element of Ni, Pd, andPt is added thereto. Ni, Pd, and Pt are the elements that belong togroup 10 of the periodic law. The inventors of the present inventionconfirmed by experiment an effect in which, by adding an appropriateamount of such an element to Al, the etching rate (etching speed) of anAl alloy with respect to an alkaline chemical solution became faster.

FIG. 5 is a graph indicating a relation between a composition ratio(additive amount) of Ni, Pd, and Pt of an Al alloy in which any of Ni,Pd, and Pt is added to Al and an etching rate with respect to a TMAHorganic alkaline chemical solution. The etching rate represents a valuewhen an Al alloy is etched in an organic alkaline developing solution(liquid temperature of 23° C.) containing 2.4 wt % of TMAH.

As indicated in FIG. 5, the composition ratio of Ni, Pd, and Pt of theAl alloy is 0.5 mol %, the etching rate becomes five times faster ormore as compared with pure Al (the composition ratio is 0 mol %).Additionally, when the composition ratio of Ni, Pd, and Pt becomes 1 mol% or larger, the etching rate becomes almost saturated.

In a region where the composition ratio of Ni, Pd, and Pt is smallerthan 0.5 mol %, the etching rate largely changes, and therefore controlof the etching amount becomes difficult. At the same time, since thepresent invention provides a sufficient effect when the etching rate isfive times or more as compared with the case of pure Al, it ispreferable that the additive amount of Ni, Pd, and Pt be 0.5 mol % ormore. Further, in view of stabilizing the etching rate, it is preferableto set the additive amount to 1 mol % or more.

In contrast, when the additive amount of Ni, Pd, and Pt exceeds 10 mol%, a rate of precipitation of compound phase of AlNi, AlPd, and AlPtincreases, and this may be left as an etching residue in the alkalinedeveloping solution and may sometimes cause an etching failure.Accordingly, it is preferable to set the total additive amount of Ni,Pd, and Pt to be added to Al to 10 mol % or smaller.

In addition, although the organic alkaline developing solution having aconcentration of TMAH of 2.4 wt % is used as the etchant in thispreferred embodiment, it is preferable that the concentration of TMAH be0.2 wt % or more and 25 wt % or less while the liquid temperature rangesbetween 10° C. and 50° C. When the concentration of TMAH is less than0.2 wt %, the etching rate of the Al alloy including Ni, Pd, and Pt isdrastically reduced, making the etching difficult to perform. Incontrast, when the concentration of TMAH exceeds 25 wt %, damageincurred by the photoresist increases, which causes a concern of patterndefects.

Further, the film thickness of the first Al alloy layer 101 a is set to200 nm, and the film thickness of the second Al alloy layer 101 b formedthereon is set to 20 nm in this preferred embodiment. However, the filmthicknesses thereof are not restricted to these examples. The inventorsof the present invention confirmed by experiment that as long as thethickness of the second Al alloy layer 101 b was 40 nm or smaller, theAl wiring film 101 was formed into a substantially smooth tapered shape.When the thickness of the second Al alloy layer 101 b exceeded 40 nm,the portion of the first Al alloy layer 101 a and the portion of thesecond Al alloy layer 101 b became step-like shapes individually whichare shapes independent from each other, and deterioration in the stepcoverage characteristic when an insulating film 101 was formed on the Alwiring film 101 was observed. Accordingly, when the thickness of thefirst Al alloy layer 101 a is 200 nm, it is preferable that thethickness of the second Al alloy layer 101 b be set to 40 nm or smaller.To state it differently, it is preferable that the thickness of thesecond Al alloy layer 101 b be ⅕ or less of that of the first Al alloylayer 101 a.

Hereinafter, an example of applying the Al wiring film 101 illustratedin FIG. 1 to a TFT active matrix substrate of a liquid crystal displayapparatus will be described as a specific example of application. Ingeneral, a TFT active matrix substrate has a structure in which a pixelelectrode which is a transparent electrode and a thin-film transistor(TFT) which is a switching element for supplying an image signal to thepixel electrode are provided on a transparent insulating substrate foreach of a plurality of pixels that are arranged in a matrix pattern, anda source line SL for feeding the image signal to each TFT and a gateline GL for feeding a drive signal to each TFT are further provided.

FIG. 6 is a plan view of a structure of a principal portion (one pixelregion) of a TFT active matrix substrate according to the firstpreferred embodiment, and FIG. 7 is a cross sectional view taken along aline A-B. As illustrated in FIG. 7, the TFT active matrix substrate hasa transparent insulating substrate 1 provided thereon with a gateelectrode 2, a gate insulating film 4, a semiconductor film 5, an ohmiccontact film 6, a TFT formed of a source electrode 7 and a drainelectrode 8, a pixel electrode 12 which is a transparent conductive filmconnected to the drain electrode 8 of the TFT, and an auxiliarycapacitance electrode 3.

The ohmic contact films 6 interposed between the semiconductor film 5and the source electrode 7, and between the semiconductor film 5 and thedrain electrode 8, respectively, are a low-resistance layer of silicon(Si) added with impurities. A region in the semiconductor film 5 betweenthe source electrode 7 and the drain electrode 8 serves as a channelportion 9 in which a channel of the TFT is formed. An interlayerdielectric film 10 for protecting the channel portion 9 of the TFT isprovided on an entire surface on the transparent insulating substrate 1,and the pixel electrode 12 is connected to the drain electrode 8 througha contact hole 11 formed in the interlayer dielectric film 10. Inaddition, as illustrated in FIG. 6, the source electrode 7 is integrallyformed with a source line SL to which the source electrode 7 isconnected, and the gate electrode 2 is integrally formed with a gateline GL to which the gate electrode 2 is connected.

In the example illustrated in FIGS. 6 and 7, the Al wiring film 101illustrated in FIG. 1 is applied to the gate electrode 2, the auxiliarycapacitance electrode 3, the source electrode 7, and the drain electrode8 on the TFT active matrix substrate. This means that the gate electrode2 has a double-layer structure formed of a first Al alloy layer 2 a anda second Al alloy layer 2 b, and the auxiliary capacitance electrode 3has a double-layer structure formed of a first Al alloy layer 3 a and asecond Al alloy layer 3 b. Similarly, the source electrode 7 has adouble layer structure formed of a first Al alloy layer 7 a and a secondAl alloy layer 7 b, and the drain electrode 8 has a double layerstructure formed of a first Al alloy layer 8 a and a second Al alloylayer 8 b.

The first Al alloy layers 2 a, 3 a, 7 a, and 8 a are individually madeof either Al or an Al alloy as in the case of the first Al alloy layer101 a illustrated in FIG. 1. The second Al alloy layers 2 b, 3 b, 7 b,and 8 b are individually made of an Al alloy containing at least oneelement of Ni, Pd, and Pt as in the case of the second Al alloy layer101 b illustrated in FIG. 1.

Hereinafter, a description will be given of a method for manufacturingthe TFT active matrix substrate illustrated in FIGS. 6 and 7. FIGS. 8 to11 are diagrams of a manufacturing process of the TFT active matrixsubstrate.

First, a transparent insulating substrate 1 such as a glass substrate iscleaned using a cleaning liquid or pure water, and the gate electrode 2having a tapered shape and the gate line GL to which the gate electrode2 is connected, and the auxiliary capacitance electrode 3 are formed onthe transparent insulating substrate 1 (FIG. 8) using a method describedwith reference to FIGS. 2 to 4.

Next, the gate insulating film 4, an Si film serving as thesemiconductor film 5, and an n⁺ type Si film (Si film heavily doped withn-type impurities) serving as the ohmic contact film 6 are sequentiallyformed, the Si film and the n⁺ type Si film are subjected to patterningusing a photoengraving technique, so that a semiconductor pattern of TFTformed of the semiconductor film 5 and the ohmic contact film 6 isformed on the gate insulating film 4 (FIG. 9). At this stage, the ohmiccontact film 6 is not yet separated into a source side and a drain side.

In the process illustrated in FIG. 9 according to this preferredembodiment, first, a silicon nitride (SiN) film with a thickness of 400nm is formed as the gate insulating film 4 by the chemical vapordeposition (CVD) method under a substrate heating condition of about300° C. Thereafter, a film of amorphous silicon (a-Si) with a thicknessof 150 nm is formed as an Si film serving as the semiconductor film 5,and an a-Si film with a thickness of 50 nm added with phosphor (P) as animpurity is formed as an n⁺ type Si film serving as the ohmic contactfilm 6. Then, a positive type photoresist of a novolak resin is coatedby a slit coater or a spin coater to a thickness of 1.6 μm and isexposed using a photomask. Subsequently, the resultant is developedusing an organic alkaline chemical solution containing TMAH, and aphotoresist pattern of the pattern of the semiconductor film 5 isformed. The a-Si film and the n⁺ type a-Si film are subjected topatterning using the photoresist pattern as a mask by dry etching usinga fluorine series gas, and thereby the semiconductor pattern of the TFTformed of the semiconductor film 5 and the ohmic contact film 6 isformed. Further, the photoresist pattern is stripped off and removedusing an amine series stripping solution.

Next, the source electrode 7 having a tapered shape, the drain electrode8, and the source line SL to which the source electrode 7 is connectedare formed on the gate insulating film 4, the semiconductor film 5, andthe ohmic contact film 6 (FIG. 10) by the method described withreference to FIGS. 2 to 4.

Here, before removing the photoresist pattern used for patterning thesource electrode 7 and the drain electrode 8, further using the patternas a mask, the ohmic contact film 6 is etched by dry etching using a gascontaining, for example, chlorine (Cl). Through this process, the ohmiccontact film 6 is separated into a source side and a drain side. At thisstage, a portion of the semiconductor film 5 in a region from which theohmic contact film 6 is removed serves as the channel portion 9 of theTFT. The photoresist pattern is removed thereafter.

Next, a silicon nitride (SiNx) film is formed as the interlayerdielectric film 10 at a film forming temperature of 200° C. According tothis preferred embodiment, the SiN film with a thickness of 300 nm isformed by the chemical vapor deposition (CVD) method under a substrateheating condition of about 300° C.

Thereafter, a photoresist pattern with a region for forming the contacthole 11 is opened is formed using a photoengraving technique, and, usingthe photoresist pattern as a mask, the contact hole 11 is formed in theinterlayer dielectric film 10 by dry etching using a fluorine seriesgas.

Finally, a transparent conductive film is formed on the interlayerdielectric film 10 including the contact hole 11, and the resultant issubjected to patterning to form the pixel electrode 12 (FIG. 11).According to this preferred embodiment, IZO (indium oxide (In₂O₃)-zincoxide (ZnO)) is formed into a film with a thickness of 100 nm as thetransparent conductive film by sputtering using an Ar gas. A photoresistpattern is formed thereon by a photoengraving technique, and, using thephotoresist pattern as a mask, wet etching is performed using a oxalicacid series solution to form the pixel electrode 12.

By the foregoing process, the TFT active matrix substrate having astructure illustrated in FIGS. 6 and 7 is completed.

Although it is not illustrated, an alignment film made of polyimide orthe like for aligning the liquid crystal, and a spacer for securing agap from an opposing substrate provided thereon with color filters orthe like are formed on a surface of the completed TFT active matrixsubstrate. Then, the TFT active matrix substrate is bonded to theopposing substrate, the liquid crystal is injected between the twosubstrates, and the two substrates are sealed together to thereby form aliquid crystal display panel. Then, a polarizing plate, a phase plate, abacklight unit, and the like are arranged outside the liquid crystaldisplay panel to complete the liquid crystal display apparatus.

As in the case of this preferred embodiment, the Al wiring film 101illustrated in FIG. 1 is applied to the gate electrode 2, the auxiliarycapacitance electrode 3, the source electrode 7, and the drain electrode8 on the TFT active matrix substrate. As a result of this, the stepcoverage characteristic of the gate insulating film 4 and the interlayerdielectric film 10 is improved, and the occurrence of a reduction in thebreakdown voltage or a broken wire in the TFT active matrix substratecan be suppressed.

In this preferred embodiment, although the Al wiring film 101illustrated in FIG. 1 is applied both to the wiring layer for the gateelectrode 2 and the auxiliary capacitance electrode 3, and the wiringlayer for the source electrode 7 and the drain electrode 8, it is alsopossible to apply the Al wiring film 101 to one of these.

In particular, when the Al wiring film 101 illustrated in FIG. 1 isapplied to the source electrode 7 and the drain electrode 8, it ispreferable to use, as the first Al alloy layer 7 a, an Al alloy film towhich a rare earth metal such as neodymium (Nd), lanthanum (La), orgadolinium (Gd) is added so that an excellent contact characteristic isobtained in an interface with the ohmic contact film 6 which makescontact with lower surfaces of the source electrode 7 and the drainelectrode 8.

Further, the pixel electrode 12 is connected to the second Al alloylayer 7 b of the source electrode 7. The Al alloy film of the second Alalloy layer 7 b contains the additive element of Ni, Pd, or Pt. When theinterlayer dielectric film 10 and the like are formed at a hightemperature, the additive element agglomerates and is deposited in ansurface layer. This also provides an effect of improving a contactcharacteristic with a conductive oxide film such as IZO or ITO used forthe pixel electrode 12.

Second Preferred Embodiment

FIG. 12 is a cross sectional view of a structure of an Al wiring filmaccording to a second preferred embodiment. As illustrated in FIG. 12,an Al wiring film 201 formed on a substrate 100 according to thispreferred embodiment has a triple-layer structure including a first Alalloy layer 201 a, a second Al alloy layer 201 b, and a third Al alloylayer 201 c which are laminated in this order, and has a tapered shapein cross section with a width smaller in an upper portion thereof than awidth in a bottom portion thereof.

The first Al alloy layer 201 a is made of an Al alloy containing atleast one element of Ni, Pd, and Pt. The second Al alloy layer 201 b ismade of an Al alloy containing nitrogen (N). The third Al alloy layer201 c is made of an Al alloy containing at least one element of Ni, Pd,and Pt. The first Al alloy layer 201 a and the third Al alloy layer 201c may have an identical composition. Also, the second Al alloy layer 201b may be formed by adding nitrogen to an Al alloy which is the same asthat used for the first Al alloy layer 201 a or the third Al alloy layer201 c.

The substrate 100 serving as a base for the Al wiring film 201 may be asemiconductor substrate such as a silicon substrate, an insulatingsubstrate such as a glass substrate used for the active matrixsubstrate, or an interlayer dielectric film provided on another wiringlayer.

Hereinafter, a method for manufacturing the Al wiring film 201illustrated in FIG. 12 will be described. FIGS. 13 to 15 aremanufacturing process diagrams thereof. First, a triple-layer structureis formed on the substrate 100 by sequentially forming, by sputteringusing the Ar gas, the first Al alloy layer 201 a made of the Al alloycontaining at least one element of Ni, Pd, and Pt, the second Al alloylayer 201 b resulted from azotizing an Al alloy film, and the third Alally layer 201 c made of the Al alloy containing at least one element ofNi, Pd, and Pt (FIG. 13).

In this preferred embodiment, in view of simplifying the manufacturingprocess, the first Al alloy layer 201 a and the third Al alloy layer 201c use an Al alloy having an identical composition, and the second Alalloy layer 201 b uses an Al alloy resulted from azotizing the same Alalloy. In this case, the first Al alloy layer 201 a, the second Al alloylayer 201 b, and the third Al alloy layer 201 c can be formed by thesputtering method using a consistent identical target in theabove-mentioned sputtering process. With this arrangement, when thesecond Al alloy layer 201 b is formed, merely a process of mixing the Argas with a nitrogen gas and performing the reactive sputtering isperformed. Accordingly, a reduction in the manufacturing cost and animprovement in the productivity can be expected. It is preferable thatthe additive amounts of Ni, Pd, and Pt in the first Al alloy layer 201a, the second Al alloy layer 201 b, and the third Al alloy layer 201 c,individually, be 0.5 mol % or more and 10 mol % or less (morepreferably, 1 mol % or more and 10 mol % or less) as in the case of thesecond Al alloy layer 101 b in the first preferred embodiment.

The second Al alloy layer 201 b is a layer having a low etching ratewith respect to the organic alkaline developing solution. The etchingrate of the Al alloy with respect to the alkaline developing solution isreduced by adding atoms of nitrogen (N). It is preferable that theadditive amount of atoms of nitrogen (N) to the second Al alloy layer201 b be 10 mol % or more so that the etching rate of the second Alalloy layer 201 b is sufficiently reduced (⅕ or less of the etching rateof the first Al alloy layer 201 a and the third Al alloy layer 201 c).

However, if the additive amount of the atoms of N is excessivelyincreased, the conductivity of the second Al layer 201 b is impaired, itis preferable to limit the additive amount to such an amount by whichthe conductivity of the second Al alloy layer 201 b is maintained.Considering Ti, Cr, Mo, Ta, W, and alloys thereof which are generallyused for the wiring film of a semiconductor device as a reference, andassuming that an upper limit of a specific resistance value of thesecond Al alloy layer 201 b is 200 μΩcm, it is preferably that theadditive amount of the atoms of N be 40 mol % or less.

After the triple-layer structure formed of the first Al alloy layer 201a, the second Al alloy layer 201 b, and the third Al alloy layer 201 cis formed, a photoresist 102 having a predetermined pattern is formed onthe third Al alloy layer 201 c using a photoengraving technique (FIG.14). In this preferred embodiment, the photoresist 102 is formed bycoating and exposing a positive type photoresist of a novolak resin, andby developing using a TMAH organic alkaline chemical solution.

Here, since the Al alloy containing at least one element of Ni, Pd, andPt can be etched by the TMAH organic alkaline chemical solution, thethird Al alloy layer 201 c exposed from the photoresist 102 is etched byextending the time of the developing process of the photoresist 102. Asa result, the third Al alloy layer 201 c under the photoresist 102 isetched in a transverse direction (in-plane direction of the film), and awidth thereof becomes smaller than that of the photoresist 102. Thismeans that ends of the third Al alloy layer 201 c individually recedefrom ends of the photoresist 102.

In contrast, the second Al alloy layer 201 b which is an azotized Alalloy is highly resistant to the TMAH organic alkaline chemicalsolution, and therefore is hardly etched. Accordingly, as illustrated inFIG. 14, notches 103 having an undercut shape are formed between thephotoresist 102 and the second Al alloy layer 201 b, the under cut shapebeing caused by receding of the ends of the third Al alloy layer 201 c.

Thereafter, in wet etching using the photoresist 102 as a mask, thefirst Al alloy layer 201 a, the second Al alloy layer 201 b, and thethird Al alloy layer 201 c are simultaneously subjected to etching andpatterning, so that the Al wiring film 201 having the predeterminepattern is formed (FIG. 15). In this preferred embodiment, an etchant ofPAN series (phosphoric acid, acetic acid, and nitric acid series) isused for the wet etching.

During this process, since a notch shape is provided under thephotoresist 102, the ends of the third Al alloy layer 201 c and uppersurfaces of the second Al alloy layer 201 b and the first Al alloy layer201 a are isotropically etched. Specifically, the upper surfaces of thesecond Al alloy layer 20 lb and the first Al alloy layer 201 a areetched while the ends of the third Al alloy layer 201 c further recede.As a result, the sidewall of the Al wiring film 201 is inclined, and theAl wiring film 201 has a tapered shape with a width smaller in the upperportion than a width in the bottom portion.

Finally, by removing the photoresist 102, the Al wiring film 201illustrated in FIG. 12 is completed.

Since the Al wiring film 201 according to this preferred embodiment hasa tapered shape, it is possible to have a good step coveragecharacteristic when an insulating film is formed thereon. Accordingly,this prevents the breakdown voltage of the insulating film fromreducing, prevents the wire of the wiring film in the upper layer frombreaking, and contributes to improvement of the yield of the product.

Further, since a process of patterning the Al wiring film 201 into atapered shape can be performed during the isotropically etching of thefirst Al alloy layer 201 a, the second Al alloy layer 201 b, and thethird Al alloy layer 201 c, the tapered shape (inclination of thesidewall) of the Al wiring film 201 is hardly affected by the change ofthe composition of the etchant. Therefore, the Al wiring film 201 havinga predetermined tapered shape can be obtained easily and in a stablemanner without a need to manage the etchant stricter than in theconventional case. Accordingly, an increase in the cost incurred inmanaging the etchant can be suppressed.

In this preferred embodiment, in order to smooth the Al wiring film 201,it is preferable to set a film thickness of the third Al alloy layer 201c to ⅕ or less of a sum of film thicknesses of the first Al alloy layer201 a and the third Al alloy layer 201 c. With this arrangement, it ispossible to optimize the notch shape of the photoresist 102 after thedeveloping process and the tapered shape of the Al wiring film 201 afterpatterning.

As in the case of the Al wiring film 101 in the first preferredembodiment, the Al wiring film 201 having the triple-layer structureaccording to the second preferred embodiment can be applied to the gateelectrode 2, the auxiliary capacitance electrode 3, the source electrode7, and the drain electrode 8 of the TFT active matrix substrateillustrated in FIGS. 6 and 7.

It is also possible to use a combination of the Al wiring film 101 ofthe first preferred embodiment and the Al wiring film 201 of the secondpreferred embodiment. For example, FIG. 16 illustrates a structure of aTFT active matrix substrate in which the Al wiring film 101 of the firstpreferred embodiment is applied to the wiring layer of the gateelectrode 2 and the auxiliary capacitance electrode 3, and the Al wiringfilm 201 of the second preferred embodiment is applied to the wiringlayer of the source electrode 7 and the drain electrode 8.

Referring to FIG. 16, the gate electrode 2 and the auxiliary capacitanceelectrode 3 have a double-layer structure including a first layer (firstAl alloy layers 2 a and 3 a) made of Al or an Al alloy, and a secondlayer (second Al alloy layers 2 b and 3 b) made of an Al alloycontaining at least one element of Ni, Pd, and Pt. In contrast, thesource electrode 7 and the drain electrode 8 have a triple-layerstructure including a first layer (first Al alloy layers 71 a and 81 a)made of an Al alloy containing at least one element of Ni, Pd, and Pt,and a second layer (second Al alloy layers 71 b and 81 b) made of an Alalloy containing nitrogen, and a third layer (third Al alloy layers 71 cand 81 c) made of an Al alloy containing at least one element of Ni, Pd,and Pt.

In particular, when the Al wiring film 201 of the second preferredembodiment is applied to the source electrode 7 and the drain electrode8, the first Al alloy layers 71 a and 81 a which are the bottom layerand the third Al alloy layers 71 c and 81 c which are the upper layerare made of an Al alloy added with transition elements of group 10 ofNi, Pd, or Pt. Therefore, it is possible to obtain an excellent contactcharacteristic in an interface with the ohmic contact film 6 which makescontact with lower surfaces of the source electrode 7 and the drainelectrode 8, and further in an interface with the pixel electrode 12(conductive oxide film such as IZO or ITO) which is connected to anupper surface of the drain electrode 8.

The a-Si film is used as an example of the semiconductor film 5 of theTFT active matrix substrate described above. It is also possible to usea semiconductor of a zinc oxide (ZnO) base, or a semiconductor of anoxide base including zinc oxide (ZnO) to which gallium oxide (Ga₂O₃),indium oxide (In₂O₃), tin oxide (SnO₂), or the like is added. When sucha semiconductor film of the oxide base is used as the semiconductor film5, it is possible to obtain a TFT having higher performance where thecarrier mobility is high than in the case of using the a-Si film.

In particular, when the Al wiring film 201 of the second preferredembodiment is applied to the source electrode 7 and the drain electrode8, an excellent contact characteristic is achieved in an interfacebetween the first Al alloy layer 201 a which is an Al alloy added withNi, Pd, or Pt and the semiconductor film 5 of the oxide base. This makesit possible to obtain a TFT having higher performance.

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of theinvention.

1. A method for manufacturing a wiring film, comprising the steps of:forming a first layer made of Al or an Al alloy; forming, on said firstlayer, a second layer made of an Al alloy containing at least oneelement of Ni, Pd, and Pt and having a composition different from acomposition of said first layer; coating a photoresist on said secondlayer and performing exposure using a photomask; developing saidphotoresist after performing the exposure and etching said second layerby using an alkaline chemical solution, so that an end portion of saidsecond layer under said photoresist after the developing recedes from anend portion of the photoresist; and forming the wiring film includingsaid first and second layers by etching and patterning said first andsecond layers simultaneously by wet etching using said photoresist afterdeveloping as a mask.
 2. (canceled)